Silencer



July 9; 1929.

R. B. BOURNE S ILENCER Filed May 16, 1928 /0 [Q] j I INVENTOR.

Patented July 9, 1929.

,UNITED STATES PATENT OFFICE.

ROLAND B. BOURNE, OF HARTFORD, CONNECTICUT, ASS IGNOR, I BY IMESNIEASSIGN- MENTS, TO THE MAXIM SILENCER COMPANY, OF HARTFORD, CONNECTICUT,A. COR

1 PORATION OF CONNECTICUT.

SILENCE-R.

Application filed May 16, 1928. Serial No. 278,224.

This invention relates to devices for silencing the exhaust of internalcombustion engines, the intake of air compressors, or the like. The termsilencing is used in a broad significance, having relation to thereduction to an unofl'ensive amplitude of sound waves Whether of audibleor of subaudible frequencies. The object of the invention is to providea simple and compact device presenting a minimum of resistance to gasflow which will be effective in silencing the noise source to which itis attached.

Sound waves of the lower frequencies, either audible or subaudible,predominate in certain types of noise creating apparatus to such anextent that if they are removed the frequencies remaining areunobjectionable. The apparatus herein described is of the filter type,blocking the passage of certain low frequency sound waves whilepermitting the transmission of those of certain higher frequencies. Lowfrequency sound waves may present their disagreeable, effects directlyto the ear, in case they are above the limit of audibility; or, whilethemselves inaudible, may create disturbances by shaking buildings,rattling windows, or the like.

For attenuating such low frequency sound waves, I make use of theprinciples of the acoustic wave filter, a device capable of attenuatingsound waves of certain. frequencies and depending, for itsaction, notupon friction (or bafiiing) but upon acOustic'reac tion between suitablydisposed series and shunt elements comprising the acoustic network. Ingeneral, the series elements are formed by the main acoustic channelthrough the device, While the shunt elements comprise chambers or othercavities suitably coupled to the main acoustic channel. Variousarrangements are possible, giving correspondingly different attenuationversus frequency characteristics. The simplest of acoustic wave filtersconsists of a main acoustic channel having laterally disposed sidebranches suitably coupled, as by holes,

to the main or series passageway, at intervals along the length thereof.The side branches may be tubes or chambers, or combinations thereof.

Every acoustic wave filter has more than one pass band of frequenciesand more than one attenuation band. It is obvious, where the filter isprimarily intended as a silencer,

that the attenuation bands should be as broad as possible. Recourse ismade, therefore, in the present invention, to a disposition wherein theattenuation versus frequency characteristics of more than one acousticsystem are superimposed in such a way that there results a wide band ofsound frequencies which sufier attenuation.

Referring to the drawings:

Fig. 1 is a diagrammatic View illustrating the principle of myinvention;

Fig. 2 is a longitudinal section through one form of apparatus embodyingmy invention;

Fig. 3 1s a section'through the apparatus in the drawings as 20, 21, 22and 23, enter the common outlet acoustic channel 24 at intervals alongthe length thereof. It is to be noted that, in all the dispositionsshown in the drawings, the first cross branch encountered upon enteringthe device communicates with the outlet channel at a point farthestremoved from the final outlet, whereas the last cross branch leaving theinlet passageway communicates with the outlet channel at a point nearestthe final outlet; the intermediate cross branches being correspondinglydisposed.

The arrangement shown in Fig. 1, while primarily intended as a schematicrepresentation of my invention, may form a practical embodiment, theside branches 11, 12, etc. being formed as pipes and the side chambers16, 17, 18, 19, as cylinders surrounding the pipes and communicatingtherewith 'by means of coupling holes, slots or the like. Such anembodiment of the invention is, however, unwieldly, and the more compactarrangement of Fig. 2 is preferred;

of sheet metal secured together by welding at-their lines of contact,and hence no rivets or bolts have been shown in the drawing. Thestructure is cnifined .within a cylindrical casing 30 having headers 31and 32 at its ends. Pipes 33 and 34 leading out of these headers may beof such length as desired for attachment to the structure to besilenced, the apparatus functioning when connected in either direction.

' lVithin the cylinder 30 is a second shell 35 secured at one end to theheader 32 and spaced from the casing 30 so as to form an annularacoustic channel 36. The other end of the inner shell is closed by aheader 37 spaced from the header 31 to form a chamber 38 connecting withpassageway 36. Between the header 37 and the header 32 are threepartitions 39, 40 and 41, serving to divide the inner easing into fourspaced compartments 42, 43, 44 and 45. The number of these compartmentsmay be changed as desired, although in general the mathematical idealwill be approached more closely the higher the number. For practicalpurposes, however, four will usually be found suflicient.

Within the compartments are side branches 46, 47, 48 and 49, eachconveniently formed by a piece of sheet metal bent in circular form 50at its center, and having its sides 51 converging as is clearly shown inFig. 3. The partitions 39, 40 and 41 and the header 32 are provided withcentral holes in alignment with the circular portions 50 of the sidebranches, so that the composite structure constitutes a central circularacoustic channel 52 closed at one end by header 37 and opening outthrough pipe 34 at the other, and having side branches 46, 47, 48 and49.

These side branches are preferably angularly arranged with respect toeach other, each ofthem being advanced at a right angle from thepreceding one. The walls 51 terminate short of the inner wall of thecasing 35, leaving coupling openings 53 corresponding to the couplingopenings 15 in Fig. 1, where the side branches are coupled to theotherwise closed acoustic side chamhers. Opposite the end of each sidebranch the casing 35 is slotted at 54 to provide a short passageconnecting the annular acoustic channel 36 .with the side branches, and,through the openings 53, with the closed side chambers 42, 43, 44 and45.

It will be apparent that the structure of Figs. 2 and 3 corresponds tothe idealized case of Fig. 1 ifthe coupling openings 15 in the latter beshifted to one end of the side branches instead of being locatedcentrally. If it is desired to vary the position of the coupling openingto correspond with the nication to the side chambers being had throughcoupling holes 66 That I claim is:

1. A silencer comprising an annular acoustic channel, a central acousticchannel, a plurality of connecting side branches, and side chamberscommunicating imlividually with the side branches but otherwise closed.

v2. A silencer comprising a pair of main acoustic channels, a pluralityof side branches joining the main acoustic channels, and side chamberscommunicating individually with the side branches but otherwise closed.

3. A silencer comprising an annular acoustic channel, a central acousticchannel, a plurality of side branches longitudinally and angularlyspaced from each other, and side chambers communicating individuallywith the side branches but otherwise closed.

4. A silencer comprising a pair of cas ings, one within the other,presenting an annular acoustic channel between them, a plurality ofpartitions within the inner casing dividing itinto separatecompartments, a central acoustic channel through all of saidcompartments, walls within each of said compartments dividing, it into aside branch and a side chamber, and coupling openings from eachcompartment to the annular acoustic channel and from each side branch toits contiguous side chamber.

5. A silencer comprising apair-of casings, one within the other, topresent an annular acoustic channel between them, a plurality ofpartitions within the inner casing dividing it into separatecompartments, a sheet of converging U-form extending between each ofsaid partitions and terminating short of the inner casing, slots in theinner casing opposite theconverging portions of said sheets, and centralopenings through the partitions forming with the sheets a centralacoustic channel.

6. A silencer comprising a pair of acous tic channels, a plurality ofside branches extending therebetween and connecting to said acousticchannels at intervals along the lengths thereof, and side chamberscommunicating individually with said side branches.

7. A'silencer comprising a pair of acoustic channels, a plurality ofside branches extending therebetween and connecting to said acousticchannels at intervals along the lengths thereof, and side chamberscommunin the wa lls.

icating individually with said side branches but otherwise closed.

8. A silencer comprising an inlet acoustic channel, an outlet acousticchannel, a plurality of side branches extending therebetween andconnecting with said inlet and outlet channels at intervals along thelengths thereof, the side branch communicating with the inlet channel atthe point nearest the inlet to the silencer opening into the outletchannel at a point farthest removed from the outlet of the silencer, andside chambers communicating individually with said side branches.

9. A silencer comprising an inlet acoustic channel, an outlet acousticchannel, a

plurality of side branches extending therebetween and connecting withsaid inlet and outlet channels at intervals along the lengths thereof,so disposed that, starting from the inlet of the silencer, the sidebranches '1, 2, n,, open into the outlet channel in the order n,2, 1,viewed from the outlet'end of the outlet channel, and side chamberscommunicating individually with said side branches. R 10. A silencercomprising a pair of main acoustic channels, a plurality of sidebranches joining the main passages, said side branches varying incross-sectional area along their lengths, and side chambers coupledacoustically to the side branches but otherwise closed. e

In testimony whereof I have affixed my signature.

ROLAND B. BOURNE. I

